[clang] [clang][Sema] Track trivial-relocatability as a type trait (PR #84621)

[Daniel Anderson via cfe-commits]

DanielLiamAnderson wrote:

This would be really useful for [ParlayLib](https://github.com/cmuparlay/parlaylib). We implement our own is_trivially_relocatable which is not nearly as reliable as having the compiler do it. I support this PR's semantics; types with non-defaulted assignment operators should report false, not true.

https://github.com/llvm/llvm-project/pull/84621